Cassette for an infusion pump

ABSTRACT

A cassette which is adapted to be insertable into and removable from an infusion pump. The cassette has a housing, a length of flexible tubing supported by the housing, and a first vertically movable member disposed in the housing. The first vertically movable member has a slot formed therein, and a portion of the flexible tubing is disposed within the slot. The first vertically movable member is movable between a clamped position in which the flexible tubing is clamped to prevent any substantial liquid flow therethrough and an unclamped position in which substantial liquid flow through the flexible tubing is enabled, and a spring is provided for biasing the first vertically movable member to the clamped position. The first vertically movable member may be designed so that the closure of a door of an infusion pump in which the cassette is inserted will cause the vertically movable member to be in the unclamped position to allow liquid flow through the flexible tubing. The cassette may have means for maintaining the first vertically movable member in the unclamped position, such as a retaining pin. The cassette has a second vertically movable member with a first surface and a second surface. The first surface has a portion which is arcuate in shape and adapted to substantially conform with a path of rotation defined by the rotary pump wheel of an infusion pump. The second surface of the second vertically movable member is disposed within the aperture formed in the upper surface of the housing so that the second vertically movable member may be vertically displaced due to physical contact with the second surface of the second vertically movable member.

BACKGROUND OF THE INVENTION

The present invention is directed to a cassette for an infusion pumpwhich may be inserted into and removed from the pump.

An infusion pump is used to automatically administer liquid medicant toa patient. The liquid medicant is supplied from a source of medicant andpumped into the patient via a catheter or other injection device. Themanner in which the liquid is infused is controlled by the infusionpump, which may have various modes of infusion, such as a continuousmode in which the liquid medicant is continuously infused at a constantrate, or a ramp mode in which the rate of infusion gradually increases,then remains constant, and then gradually decreases.

Some infusion pumps utilize a cassette or module which may be insertedinto and removed from the pump. One such module is disclosed in U.S.Pat. No. 5,257,978 to Haber, et al. The module 2 disclosed in thatpatent receives a length of an intravenous line 4 in its interior, and alength of silicon tubing 78 is connected to the intravenous line 4 toform a single continuous conduit. The module 2 is insertable into aninfusion pump, in the form of a peristaltic pump 5, via a door 80 whichmay be opened and closed. The pump 5 is constructed so that it willoperate only when the door is completely closed.

SUMMARY OF THE INVENTION

The invention is directed to a cassette which is adapted to beinsertable into and removable from an infusion pump. In one aspect, theinvention is directed to a cassette having a housing, a length offlexible tubing supported by the housing, and a vertically movablemember disposed in the housing. The vertically movable member has a slotformed therein, and a portion of the flexible tubing is disposed withinthe slot. The vertically movable member is movable between a clampedposition in which the flexible tubing is clamped to prevent anysubstantial liquid flow therethrough and an unclamped position in whichsubstantial liquid flow through the flexible tubing is enabled, and aspring is provided for biasing the vertically movable member to theclamped position.

The housing may have an upper surface with an aperture formed therein,and the vertically movable member may have an upper portion whichextends through the aperture to an elevation higher than the uppersurface of the housing when the vertically movable member is disposed inthe clamped position, so that the closure of a door of an infusion pumpin which the cassette is inserted will cause the vertically movablemember to be in the unclamped position to allow liquid flow through theflexible tubing.

The cassette may have means for maintaining the vertically movablemember in the unclamped position, such as a retaining pin. The retainingpin may be insertable in a first bore formed in the vertically movablemember and a second bore formed in the housing. The cassette housing maybe provided as a compact housing having a length, a width, and a height,wherein the length of the housing is about six times the height of thehousing, and wherein the height of the housing is about twice the widthof the housing.

In another aspect, the invention is directed to a cassette adapted to beinsertable into an infusion pump having a rotary pump wheel andremovable from the infusion pump. The cassette in accordance with thisaspect has a housing with a length, a width, and a height and an uppersurface with an aperture formed therein. The length of the housing is atleast about five times the height of the housing, and the height of thehousing is at least about twice the width of the housing. A length offlexible tubing is supported by the housing.

The cassette has a vertically movable member with a first surface and asecond surface. The first surface has a portion which is arcuate inshape and adapted to substantially conform with a path of rotationdefined by the rotary pump wheel of the infusion pump. The secondsurface of the vertically movable member is disposed within the apertureformed in the upper surface of the housing so that the verticallymovable member may be vertically displaced due to physical contact withthe second surface of the vertically movable member.

These and other features and advantages of the present invention will beapparent to those of ordinary skill in the art in view of the detaileddescription of the preferred embodiment, which is made with reference tothe drawings, a brief description of which is provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an ambulatory infusion pump and a firsttype of cassette which is insertable into the pump;

FIG. 2A is a cross-sectional front view of a portion of the infusionpump of FIG. 1 with the cassette disposed therein;

FIG. 2B is a cross-sectional side view of a portion of the infusion pumpof FIG. 1 with the cassette disposed therein;

FIG. 3A is a cross-sectional front view of a portion of the infusionpump of FIG. 1 with a second type of cassette disposed therein;

FIG. 3B is a cross-sectional side view of a portion of the infusion pumpof FIG. 1 with the second type of cassette disposed therein;

FIG. 4A is a cross-sectional side view of the first type of cassette inwhich a flexible tube is clamped;

FIG. 4B is a top view of the cassette of FIG. 4A;

FIG. 5A is a front elevational view of a platen which forms part of thecassette of FIG. 4A;

FIG. 5B is a side elevational view of the platen of FIG. 5A;

FIG. 6 is cross-sectional side view of a portion of the infusion pump;

FIG. 7 is a block diagram of the electronic components of the infusionpump of FIG. 1;

FIGS. 8A-8C illustrate various embodiments of the cassette sensor shownschematically in FIG. 7;

FIG. 9 is a flowchart of the overall operation of the infusion pump;

FIG. 10 is a flowchart of the ready-to-run step shown schematically inFIG. 9;

FIG. 11 is a flowchart of the operating system utilized by the infusionpump;

FIG. 12 is a flowchart of a turn-off routine performed during theoperation of the infusion pump;

FIGS. 13A-13C are flowcharts of three sensor routines performed duringthe operation of the infusion pump;

FIG. 14 is a flowchart of a backlight routine performed during theoperation of the infusion pump; and

FIG. 15 illustrates a number of data-recording steps performed duringthe operation of the infusion pump.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A preferred embodiment of a battery-powered, ambulatory infusion pump 10in accordance with the invention is illustrated in FIG. 1 along with afirst type of cassette 12 which is insertable into the pump 10. Theportable pump 10 may be carried in a pouch or other device (not shown)attached to a patient so that the pump 10 may be carried wherever thepatient goes.

The infusion pump 10 has a keypad 14 via which a user may input data andcommands, a selectively backlighted, dot matrix display 16 fordisplaying textual messages to the user, a light sensor 18 for detectingthe level of ambient light, and a pair of light-emitting diodes (LED)20, a green LED for indicating the normal operation of the pump 10 and ared LED for indicating an alarm or abnormal operating condition of thepump 10. As described below, the level of light sensed by the ambientlight sensor 18 is used to control when the display 16 is backlighted.

A door 30 is pivotally attached to the upper portion of the infusionpump 10 via a number of hinges 32. The underside of the door 30, whichis shown in FIG. 1, has a pair of slots formed therein in which a pairof metal rods 35 are fixed. As described below, each of the metal rods35 selectively engages a pair of slidable latching members to retain thedoor 30 in the closed position during operation of the pump 10.

An arcuate metal leaf spring 36 is disposed on the underside of the door30. The two ends of the leaf spring 36 are anchored by a pair ofretaining elements 38 fixed to the door 30. When the cassette 12, inwhich a flexible silicon tube 40 is disposed, is inserted into the pump10 and the door 30 is closed, the leaf spring 36 makes contact with andapplies a downward force on the upper surface 42 of a vertically movableplaten 44. As shown in FIGS. 1 and 4B, the upper surface 42 of theplaten 44 is disposed within an elongated slot or aperture 43 disposedin the upper surface of the cassette housing 12. The platen 44 has alower curved surface 46 against which the flexible tube 40 is pressed bya number of rollers 48 disposed on a conventional rotary pump wheel 49(see FIG. 2A) to facilitate pumping of liquid through the tube 40. Therotary pump wheel 49 is fixed to a gear 50 (FIG. 2B) which is driven bya drive belt (not shown) connected to a DC motor 51 (FIG. 7) via a geardrive assembly (not shown).

Liquid is supplied to the tube 40 via a supply tube 52 connected to asource of liquid, which may be a liquid supply container or bag (notshown) fixed to the housing of the pump 10. The liquid is infused intothe patient via a catheter or other injection device (not shown) fluidlyconnected to a length of tubing 54 fluidly connected to the tube 40. Thetubing 52, 54 may comprise conventional polyvinylchloride (PVC) tubinghaving an outside diameter slightly larger than the inside diameter ofthe flexible tube 40 so that the tubing 52, 54 may be inserted into theflexible tube 40 to effect a liquid-tight seal.

The tubing 52, 54 may be solvent-bonded to the cassette housing 12,which is plastic, to prevent the tubing 52, 54 from being inadvertentlypulled from the tube 40. As shown in FIG. 4A, the bottom portion of thecassette 12 has two semi-circular retaining members 56 integrally formedtherewith, each of which abuts a portion of the flexible tube 40 whereit overlaps the tubing 52, 54 to further prevent the tubing 52, 54 frombeing inadvertently pulled from the tube 40. A second pair of similarsemi-circular retaining members are integrally formed with the pumphousing at a point directly below the retaining members 56, as shown inFIGS. 2A and 3A, for the same purpose.

The cassette 12 has a flow-stop mechanism 60 that automatically clampsthe flexible tube 40 shut when the cassette 12 is not disposed in thepump 10 or when the pump door 30 is open. The flow-stop mechanism 60,which is shown in detail in FIGS. 2A and 2B, has a housing 62 in which avertically displaceable flow-stop member 64 and a spring 66 aredisposed. As shown in FIG. 2B, the flexible tube 40 passes through aslot 68 formed in the flow-stop member 64, and the spring 66 biases theflow-stop member 64 upwardly.

While the cassette 12 is disposed in the pump 10 with the door 30closed, one of the spring retaining members 38 makes contact with anupper surface 70 of the flow-stop member 64, thus preventing the spring66 from forcing the flow-stop member 64 upwards enough to cause theflexible tube 40 to be flattened by the bottom surface of the slot 68.When the door 30 is opened, or when the cassette 12 is not disposedwithin the pump 10, the spring 66 forces the flow-stop member 64 upwardsa distance sufficient to flatten the flexible tube 40, as shown in FIG.4A, so as to prevent any liquid flow therethrough.

When the cassette 12 is in the pump 10, as the pump door 30 is closed,one of the rollers 48 of the rotary pump wheel 49 will make contact withthe flexible tube 40, causing it to be clamped shut, as shown in FIGS.2A and 3A, and then subsequently, as the door 30 closes further, theflow stop member 64 will be forced downwards, unclamping the flexibletube 40. Thus, the tube 40 will be clamped at all times, either by oneof the rollers 48 or by the flow stop member 64. Similarly, as the door30 is opened, the flow stop member 64 will clamp the flexible tube 40before the roller(s) 48 of the rotary pump wheel 49 unclamp the tube 40,thus preventing any liquid free-flow through the tube 40.

When the cassette 12 is not inserted into the pump 10, the flow-stopmechanism 60 may be disabled by manually aligning a bore 74 (FIG. 2B) inthe flow-stop housing 62 with a bore 76 in the flow-stop member 64 andinserting a pin 78 (see FIG. 1) into the aligned bores 74, 76. Whenplaced in the bores 74, 76, the pin 78 will prevent the flow-stop member64 from being displaced upwardly by the spring 66, and thus prevent theflexible tube 44 from being flattened and the liquid flow from being cutoff.

FIGS. 3A and 3B illustrate a second type of cassette, which is showndisposed within the infusion pump 10. The only difference between thetwo types of cassettes 12 is the size and shape of the bottom portion ofthe flow-stop member 64. The bottom portion of the flow-stop member 64of the first type of cassette 12, shown in FIGS. 2A and 2B, is generallyspherical and does not extend outside of the flow-stop housing 62. Thebottom portion of the flow-stop member 64 of the second type of cassette12, shown in FIGS. 3A and 3B, has a downwardly angled finger 82 thatextends through a circular bore 84 disposed in the bottom of theflow-stop housing 62.

Referring to FIGS. 4A and 4B, the cassette 12 has a length L ofapproximately 9.7 centimeters (cm), a height H of approximately 1.5 cm,and a width W of approximately 0.8 cm. The outer diameter of theflexible tube 40 (when undistorted) is approximately 0.4 cm.

The upper surface 42 of the platen 44, which is shown in FIGS. 4A and4B, has an elongated central aperture 86 formed therein and is slightlycurved to generally conform to the arcuate shape of the leaf spring 36.As shown in FIGS. 5A and 5B, the platen 44 has a bottom portion 90 and atop portion 92, the bottom portion 90 being wider than the top portion92. The top portion 92 of the platen 44 is loosely disposed within theslot 43 (FIG. 4B) formed in the cassette 12 and is retained in the slot43 only by the presence of the flexible tube 40 beneath the bottom ofthe platen 44, as shown in FIG. 4A.

The infusion pump 10 has a latching mechanism 100, illustrated in FIG.6, for retaining the door 30 in its closed position. Referring to FIG.6, the latching mechanism 100 includes a pair of horizontally slidablemetal plates 102a, 102b which are supported by a flat portion of arotary pump wheel housing 104 and a pair of support beams 106. Each ofthe metal plates 102a, 102b has a respective pair of curved latchmembers 108a, 108b integrally formed therewith. A pair of independentlyoperable door-release buttons 110a, 110b are disposed on either side ofthe infusion pump 10. Each door-release button 110a, 110b has a hollowcylindrical body portion 112a, 112b and a central member 114a, 114bdisposed within the hollow body portion 112a, 112b. Each of the centralmembers 114a, 114b engages a respective end of one of the slidableplates 102a, 102b. A pair of annular slots 116a, 116b are formed in thebody portions 112a, 112b, and a pair of ridges 118a, 118b integrallyformed with the pump housing are disposed within the slots 116a, 116b tolimit the horizontal displacement of the door-release buttons 110a,110b.

Each of the slidable plates 102a, 102b has a respective central aperture120a, 120b disposed therein, and a spring 122 is disposed within boththe of central apertures 120a, 120b so as to spring-bias or force eachof the slidable plates 102a, 102b against the central member 114a, 114bof the door-release button 110a, 110b with which the end of the slidableplate 102a, 102b makes contact. The spring 122 may be retained withinthe apertures 120a, 120b by an L-shaped retaining member (not shown).

As shown in FIG. 6, the two curved latches 108a, 108b of each of theplates 102a, 102b engage both of the rods 35 fixed to the underside ofthe pump door 30, due to the force of the spring 122, thus preventingthe door 30 from being opened. Each plate 102a, 102b alone is sufficientto keep the door 30 closed. To open the door 30, both of thedoor-release buttons 110a, 110b must be simultaneously depressed, inwhich case the slidable plates 102a, 102b are moved, against the forceof the spring 122, to cause the curved latches 108a, 108b to disengagethe metal rods 35, thus allowing the door 30 to be opened. The door 30may be provided with a spring or other means (not shown) to cause thedoor 30 to open automatically when both of the door-release buttons110a, 110b are pressed. Since both of the door-release buttons 110a,110b must be actuated to open the door 30, any inadvertent opening ofthe door 30 due to the infusion pump 10 being dropped or jarred isreduced or eliminated.

A block diagram of the electronics of the infusion pump 10 is shown inFIG. 7. Referring to FIG. 7, the infusion pump 10 includes a controller200 with a built-in analog-to-digital (A/D) converter 200a, anelectrically programmable read-only memory (EPROM) 204 having a built-ininput/output (I/O) interface 204a, a random-access memory (RAM) 208, areal-time clock 210 and the display 16, all of which are interconnectedby a communications bus 212. The display 16 has a backlight 220 which isselectively activated by an enable signal generated on a line 222interconnecting the controller 200 and the backlight 220. Both the RAM208 and the real-time clock 210 are connected to a battery 214 whichsupplies power to them only in the absence of system power (generated bya second battery 282). Since it is always powered, the RAM 208 is anon-volatile memory.

The controller 200, which may be a conventional microcontroller such asan 80C196KB commercially available from Intel Corporation, controls anaudible alarm generator 230 via a line 232, the LEDs 20 via a line 234,and an amplifier circuit 236 via a line 238. The amplifier circuit 236is connected to drive the pump motor 51 which drives the rotary pumpwheel 49. During normal operation, the controller 200 also sends aperiodic signal to a conventional watchdog timer 250 via a line 252. Ifthe controller 200 should fail to transmit the periodic signal to thewatchdog timer 250, which would indicate failure or malfunction of thecontroller 200, the watchdog timer 250 transmits a signal via a line 260to cause the alarm 230 to sound, transmits a signal via a line 262 tocause the red LED to be illuminated, and transmits a signal via a line264 to the amplifier circuit 236 to cause the pump motor 51 to stop.

The pump 10 has a number of sensors which sense various conditionsrelating to the operation of the pump. These sensors include an inputpressure sensor 270 for detecting the liquid pressure within theflexible tube 40 at a point upstream of the rotary pump wheel 49 and anoutput pressure sensor 272 for detecting the liquid pressure within theflexible tube 40 at a point downstream of the rotary pump wheel 49. Theinput pressure sensor 270 generates an analog signal, indicative of theinput pressure, which is transmitted to the A/D converter 200a via aline 274, and the output pressure sensor 272 generates an analog signal,indicative of the output pressure, which is transmitted to the A/Dconverter 200a via a line 276. Each of the pressure sensors 270, 272,which detect occlusions with the flexible tube 40 or the tubing 52, 54connected thereto, may be provided in the form of a strain gauge or beam(not shown) which is in contact with the exterior of the flexible tube40 and a high-gain amplifier (not shown) connected to the strain beam.

The pressure sensors 270, 272 are connected to and receive power from apower switch 280 which is connected to a battery 282 through a systempower switch 284, a voltage regulator 286, and a system power line 287.The system power switch 284 selectively supplies power from the battery282 to the voltage regulator 286 based on the state of a pump on/offswitch 288 connected to the system power switch 284. The power switch280 is controlled by the controller 200 via the bus 212, the I/Ointerface 204a, and a line 294 which interconnects the I/O interface204a and the power switch 280.

The pump 10 has an air-in-line sensor 300, which may be provided in theform of a conventional piezoelectric transmitter and receiver (notshown) coupled to a sensing circuit (not shown), to detect the presenceof any significant air bubbles within the flexible tube 40. Theair-in-line sensor 300 receives power from a power switch 302 which isconnected to the system power line 287 and controlled by the controller200 via a line 304 connected to the I/O interface 204a.

The pump 10 has a shaft encoder sensor 308 and a Hall-effect sensor 310which receive power from a power switch 312 coupled to the system powerline 287 and controlled by the controller 200 via a line 314. The shaftencoder sensor 308, which is disposed on the shaft of the motor 51, maybe a two-phase motion sensing encoder which provides two signal outputsto the controller 200. The rotational speed of the motor 51 and itsdirection of rotation are determined by the controller 200 based uponthe rate and phase relationship between the two signal outputs. TheHall-effect sensor 310 is disposed adjacent the rotary pump wheel 49 anddetects magnetic encoding on the pump wheel 49 for detecting rotation ofthe wheel 49.

A cassette sensor 320, which is also connected to the power switch 312,detects the type of cassette which is inserted into the pump 10. Asdescribed below, the pump 10 may accept different types of cassettes andtake different operating actions based upon the type of cassette whichis inserted. Various possible embodiments of the cassette sensor 320 areshown in FIGS. 8A-8C. Each embodiment includes a force-sensitiveresistive element 322 disposed in a sensing circuit. The circuits ofFIGS. 8A and 8B act as force-to-voltage converters (the amplifier 323 inFIG. 8B is an operational amplifier), and the circuit of FIG. 8C (whichincludes a Schmidtt trigger 324) acts as a force-to-frequency converter.

The force is generated by the physical contact between the downwardlyangled finger 82 of the second type of cassette 12 shown in FIGS. 3A and3B and the force-sensitive resistive element 322 when the cassette 12 isinserted into the pump 12 and the door 30 is closed. Since the firsttype of cassette 12 shown in FIGS. 2A and 2B has no downwardly extendingfinger, the insertion of that type of cassette does not result in anyphysical contact with the force-sensitive resistive element 322. Thus,the resistance of the resistive element 322 changes only when the secondtype of cassette 12 is inserted, thus causing the cassette sensor 320 togenerate an electrical signal (a voltage signal in the cases of FIGS. 8Aand 8B and a frequency signal in the case of FIG. 8C) indicative of thetype of cassette inserted on a line 325 connected to the I/O interface204a. The force-sensitive resistive element 322 is a conventionalcomponent which is commercially available from Interlink Electronics ofCarpinteria, Calif. As described below, other types of sensors may beutilized.

Referring to FIG. 7, the ambient light sensor 18 is connected to a powerswitch 326 which is controlled by the controller 200 via a line 328 fromthe I/O interface 204a. Signals generated by a door-open sensor 330, abolus infusion request switch 332, and the keypad 14 are transmitted tothe controller 200 via the I/O interface 204a. Although not shown inFIG. 7 for purposes of simplicity, the controller 200, the EPROM 204,the RAM 208 and the display 16 are also connected to and receive powerfrom the system power line 287.

The operation of the infusion pump 10 is controlled by a computerprogram stored in the EPROM 204 and executed by the controller 200. Aflowchart of the overall operation is illustrated in FIG. 9. Referringto FIG. 9, when the pump 10 is turned on via the on/off switch 288, atstep 402 the pump is initialized and a test of the pump operation isperformed. The pump 10 may be turned off temporarily during an infusion,in which case the pump 10 may continue the infusion when it is turnedback on, as described below. At step 404, if there is any remainingvolume of liquid to be infused by the pump or any additional timeremaining for an infusion, which would be the case where the pump wastemporarily turned off during an infusion, the program branches to step406, where the user is asked, via a message displayed on the display 16,whether the previous infusion should be resumed. If the user answers yes(via the keyboard 14), the program branches to a ready-to-run step 410.If the previous infusion is not to be resumed, the program branches tostep 412.

The infusion pump 10 has a lockout mode in which the user may beprevented from programming the infusion parameters, such as the volumeto be infused or the rate of infusion. For example, the pump 10 could beprogrammed by a medical assistant to deliver a particular infusionhaving a particular flow profile, flow rate and volume to be infused.After programming that infusion, the medical assistant could place thepump in lockout mode, which would prevent the patient from changing anyof the infusion parameters. At step 412, if the pump 10 has beenpreviously placed in lockout mode, the program branches directly to theready-to-run step 410, bypassing all programming steps.

At step 412, if the pump is not in lockout mode, the program branches tostep 414, at which point the program prompts the user, via the display16, to input whether the patient should be allowed to program the pumpduring the subsequent infusion. If the pump is not to be programmable,the program branches to step 416 where a lockout sequence is performedby requesting the user to input which infusion modes should be lockedout. If the pump is to be programmable by the patient, the programbypasses step 416.

The infusion pump 10 has five basic modes of infusion: 1) a continuousmode in which the pump delivers a single volume at a single rate; 2) anauto-ramp mode in which the pump delivers liquid at a rate thatgradually increases to a threshold rate, stays constant at the thresholdrate, and then gradually decreases; 3) an intermittent mode in which thepump delivers discrete liquid volumes spaced over relatively longperiods of time, such as a liquid volume every three hours; 4) a custommode in which the pump can be programmed to deliver a unique infusionrate during each of 25 different time periods; and 5) a pain-controlledanalgesic (PCA) mode during which the pump will periodically infuseboluses of analgesic in response to periodic requests by the patient,which requests are made via the bolus-request key 332.

At step 418, the pump 10 generates on the display 16 the prompt"Continuous?" to the user. If the user desires to use the pump in itscontinuous mode, the user answers "yes" via the keypad 14, and theprogram branches to step 420 at which the continuous mode is programmedby the user by entering a number of infusion parameters, such as thedesired infusion rate, the volume to be infused, etc. At step 418, ifthe user does not want to use the continuous mode, the user answers"No," and the program branches to step 422. Steps 422-436 are generallythe same as steps 418 and 420, except that the user may be prompted fordifferent infusion parameters, depending on which of the five possibleinfusion modes is selected.

After the completion of one of the steps 420, 424, 428, 432, or 436, theprogram branches to the ready-to-run step 410, a flowchart of which isshown in FIG. 10. Referring to FIG. 10, the ready-to-run step 410includes a step 440 at which the infusion rate and the volume to beinfused which were entered during one of the programming steps 420, 424,428, 432, 436, are shown on the display 16. Then the program waits atstep 442 until the "Run" key of the keypad 14 is pressed, at which pointthe program branches to step 444 where the cassette sensor 320 ischecked to determine which type of cassette has been inserted into theinfusion pump 10.

The infusion pump 10 has the capability to alter its operation basedupon the type of cassette 12 which is inserted into the pump 10, asdetermined by the cassette sensor 320. In one embodiment, the insertionof the cassette 12 shown in FIGS. 3A-3B, which is referred to herein asa "micro-set," prevents the infusion pump 10 from performing an infusionif the programmed infusion rate exceeds a predetermined limit. In thisembodiment, at step 446, if a micro-set has been installed, the programbranches to step 448 where the infusion rate parameters entered duringone of the programming steps 420-436 are checked. At step 450, if theprogrammed infusion rate exceeds the predetermined limit, which may be99.9 milliliters/hour, the program branches to step 452 where the pumpgenerates a message on the display 16 to that effect and branches backto step 440 upon any key being pressed at step 454. If a micro-set wasnot installed as determined at step 446, the program skips steps 448-454and branches directly to the run mode 460 shown in FIG. 9.

Referring back to FIG. 9, during the run mode 460, the pump 10 infusesthe patient with a liquid medicant in accordance with the infusion modeselected at one of steps 418, 422, 426, 430, 434 and the infusionparameters entered at one of steps 420, 424, 428, 432, 436. The pump 10remains in the run mode 460 until the hold key is pressed, as determinedat step 462. Upon the occurrence of an alarm condition, an alarm isreported at step 464.

At step 462, if the hold key is pressed, the infusion is stopped at step466, and the pump 10 waits for the run key to be pressed at step 468 orthe on/off switch to be turned off at step 470.

Summarizing the operation described above, if the pump is to be utilizedin lockout mode, a medical assistant turns the pump on, programs thedesired infusion mode at one of steps 420, 424, 428, 432, 436, and thenturns the pump off. The programmed infusion parameters will be retainedin the nonvolatile memory 208. The medical assistant would then turn thepump back on, press the "No" key in response to the "Programmable?"prompt at step 414, enter the lockout information at step 416, and thenturn the pump off again. When the patient subsequently turned on thepump to perform the infusion (after a cassette 12 is primed with theliquid to be infused and inserted into the pump), the program wouldproceed from step 412 directly to the ready-to-run step 410, which wouldprevent the patient from altering the infusion parameters.

If the lockout mode was not utilized, the medical assistant or thepatient could turn the pump on, program the desired infusion mode, andthen press the "Run" key to start the infusion without ever turning thepump off.

The ability of the pump to take different actions based upon the type ofcassette inserted into the pump could be utilized in many ways. Forexample, the pump could be utilized with any of four different types ofcassettes, and the pump could be preprogrammed with a unique infusionmode and/or a unique set of infusion parameters for each type ofcassette.

The different infusion modes could be based on the liquid medicant to beinfused. For some liquid medicants, it may be desirable to utilize theauto-ramp mode of infusion so as not to "shock" the patient by startingthe infusion at a relatively large flow rate. These liquid medicantswould be used with a type of cassette that, when inserted into the pump,would cause the pump to automatically set the infusion mode to theauto-ramp mode. Thus, in this example, the program illustrated in FIG. 9would branch from step 414 directly to step 424 without any interveningprogramming steps. For other liquid medicants, the continuous mode ofinfusion may be appropriate. The infusion parameters entered at one ofsteps 420, 424, 428, 432, 436 could also be customized based upon thetype of cassette inserted and/or the liquid medicant to be infused.

Different types of cassettes could be distinguished by the pump 10 basedupon the length (or flexibility) of the flow-stop member (which couldhave four slightly different lengths or flexibilities), so that fourdistinct forces would be generated on the force-sensitive resistiveelement 322, or in a conventional manner based upon other structuralfeatures of the cassette.

For example, two light detectors could be disposed side by side in thetop portion of the pump, each light detector having a transmitter whichtransmits a light beam to an associated receiver. Each cassette could beuniquely identified by the presence (or absence) of two notches, eachnotch being positioned adjacent one of the light detectors. Each lightdetector would detect the presence of a notch because the light beamwould be uninterrupted when the cassette was inserted into the pump,whereas the absence of a notch would cause the light beam to beinterrupted upon insertion of the cassette. Thus, the use of two lightdetectors and two associated notch locations would allow detection offour different types of cassettes, thus allowing four pre-programmedmodes of pump operation.

A flowchart of the operating system 500 of the infusion pump 10 isillustrated in FIG. 11. The operating system 500 determines how theoperations and tasks shown in the flowchart of FIG. 9 are performed.

If the pump is in the run mode 460 shown in FIG. 9 and the pump isinfusing at a relatively low flow rate, the pump may operate in a sleepmode which utilizes a relatively low rate of power consumption from thebattery 282, such as 50 microamperes. When in the sleep mode, thecontroller 200 does not execute any instructions of the computerprogram, and its internal clocks are turned off. The pump isperiodically placed in an idle mode which utilizes an intermediate rateof power consumption, such as 8 milliamperes. When the pump is in theidle mode, the controller 200 does not execute any instructions of thecomputer program, but its internal clocks continue to run. If the pumpis in neither the sleep mode nor the idle mode, the computer program isexecuted and the internal clocks in the controller 200 run. In thisoperating mode, power is consumed at a relatively high rate, such as 17milliamperes.

Referring to FIG. 11, if the pump is not operating in the run mode 460as determined at step 502, the program branches to step 504 where any ofthe processing tasks of steps 402-436 of FIG. 9 may be performed. Asdescribed above, these tasks relate to the initial programming of theinfusion pump 10 and are user-interactive. When there are no more ofsuch tasks to be performed, for example, where the user has pausedduring the programming of the pump or has completed the pumpprogramming, the program branches to step 506, where the controller 200is placed in its idle mode, described above, via a software command. Thecontroller 200 exits the idle mode upon the generation of an interruptthat is generated at step 508. The interrupt is periodically generatedby the controller 200, for example, every 20 milliseconds.

Thus, when the pump is not in the run mode 460, the program cyclesthrough steps 502-508 where it alternately performs at step 504 one ormore of the processing tasks shown at steps 402-436 in FIG. 9 and isidled at step 506 to conserve battery power.

Under certain conditions, the pump may operate in the sleep modedescribed above. The pump may operate in the sleep mode when it is inthe run mode 460 (FIG. 9) and is pumping below a relatively low infusionrate threshold, such as five milliliters/hour.

To deliver such a low infusion rate, the motor 51 is not activatedcontinuously, but is instead turned on periodically (the motor 51 has aminimum rate at which it must be driven or else it will stall) todeliver a relatively small volume of liquid medicant, 50 microliters forexample, and then is turned off. It is when the motor 51 is turned offwhen the controller 200 is placed in the sleep mode. When the programmedinfusion rate is below the threshold, the frequency with which the motorturns on and off is determined by the programmed infusion rate. If theprogrammed infusion rate is above the threshold, the motor 51 will pumpcontinuously.

Referring to FIG. 11, at step 510, if the pump is not in a stealth mode(described below), the program branches to step 512 where a number ofprocessing tasks relating to the infusion may be performed. At step 514,the watchdog timer 250 is strobed, and at step 516 the programdetermines whether the controller 200 may be placed in the sleep mode.As described above, the controller 200 may be placed in the sleep modeif the infusion rate is less than a predetermined threshold rate. Thereare also other conditions which must be satisfied. For example, themotor 51 cannot be active, an audio beep (in response to a key beingpressed for example) cannot be active, no timed functions can be active(such as a timed LED illumination), the backlight 220 cannot be on, andthe display 16 cannot be scrolling text. If these conditions aresatisfied, the program branches to step 520 where the power to a numberof sensors is turned off, and to step 522 where the controller 200 isplaced in its sleep mode.

The controller 200 remains in the sleep mode until it is "awakened" byany of three occurrences: 1) any key being pressed, including thebolus-request key 332; 2) the watchdog timer timing out; or 3) aone-second strobe generated by the real-time clock 210. In the absenceof conditions 1) and 2), the controller 200 will be awakened everysecond by the strobe from the real-time clock 210. Upon being awakened,the internal clocks of the controller 200 are started at step 524, andthe program branches to step 508 where it waits for the next 20 msinterrupt generated by the controller 200.

The infusion pump 10 also has a stealth mode relating to theintermittent infusion mode of FIG. 9. In this mode, the pump 10 deliversan infusion spaced at relatively large time intervals, such as minutesor hours. Between infusions, the pump is placed in a stealth mode inwhich the controller 200 is put to sleep.

FIG. 12 illustrates an off-control routine 530 that is periodicallyinvoked to determine whether the on/off switch 288 (FIG. 7) of theinfusion pump 10 has been turned off. In that case, as determined atstep 532, the program branches to step 534 where it determines if it isokay to turn the pump off (it is okay to turn the pump off as long as itis not in the run mode 460). If it is okay to turn the power off, theprogram branches to step 536. If the pump is not in the intermittentmode as determined at step 536, the power is turned off. If the pump isin the intermittent mode, the program branches to step 538, whichdetermines whether there are any more periodic doses (infusions) to bemade. If there are no more doses, the power is turned off.

If there is at least one additional dose, the pump is placed in thestealth mode at step 540. Referring back to step 510 of FIG. 11, if thepump is in the stealth mode, the program branches to step 550, whichdetermines whether the next dose in the intermittent mode is scheduledwithin the next 30 minutes. If not, the program branches to steps520-522 where the controller 200 is put to sleep.

If the next dose is within 30 minutes as determined at step 550, theprogram branches to step 552, where it determines whether the time untilthe next dose, or the time after that dose if not given, is a multipleof ten minutes. If it is, then the program branches to step 554, wherethe pump 10 generates an audible beep to the user as a reminder that thenext dose is a multiple of ten minutes away. Thus, when the intermittentinfusion mode is being used and the pump is in the stealth mode, thepatient is given three audible warnings that the next dose is imminent,a first warning at 30 minutes prior to the dose, a second warning at 20minutes prior to the dose, and a third warning at 10 minutes prior tothe dose. If the next dose is not given on schedule, a fourth warning isgenerated at the time of the dose, and three additional warnings, spaced10 minutes apart, are given after the time for the dose.

During the operation of the infusion pump 10, a number of the sensorsused to sense various conditions may be turned on only when they areactive in order to conserve battery power. The sensors that areselectively turned on include the input pressure sensor 270, the outputpressure sensor 272, the air-in-line detector 300, the shaft encoder308, the Hall-effect sensor 310 and the ambient light sensor 18. Thesepowering of these sensors is controlled by a number of computer programroutines, three of which are illustrated in FIGS. 13A-13C.

Referring to FIG. 13A, a pressure sensor routine 600 may be used for theselective powering of the input and output pressure sensors 270, 272. Ifit is time to check either the input pressure or the output pressure inthe flexible tube 40 as determined at step 602, the power supplied toboth pressure sensors 270, 272 is turned on at step 604 via the line 294to the power switch 280. The program then delays (e.g. a delay of 20 ms)at step 606 to allow the sensors 270, 272 to stabilize, and then thesensed pressure is read at step 608, following which both sensors 270,272 are turned off at step 610 via the control line 294 to the powerswitch 280.

Referring to FIG. 13B, a sensor routine 620 may be used for theselective powering of the shaft encoder 308 of the motor 51. The shaftencoder 308 is active only when the motor 51 is turning, as determinedat step 622. If it is time to turn the motor 51, the power supplied tothe shaft encoder 308 is turned on at step 624 via the control line 314to the power switch 312. The program then delays at step 626 to allowthe shaft encoder 308 time to stabilize, after which time the shaftencoder 308 will automatically generate signals indicative of therotational rate and direction of the motor shaft. When the motor stopsturning, as determined at step 628, the power to the shaft encoder 308is turned off at step 630 via the control line 314 to the power switch312.

Referring to FIG. 13C, a sensor routine 640 may be used for theselective powering of the air-in-line sensor 300. If it is time to checkthe air-in-line sensor 300 as determined at step 642, the power suppliedto the air-in-line sensor 300 is turned on at step 644 via the line 304to the power switch 302. The program then delays (e.g. a delay of 2 ms)at step 646 to allow the sensor 300 to stabilize, and then the sensor300 is read at step 648, following which the sensor 300 is turned off atstep 650 via the control line 304 to the power switch 302. The routinesshown in FIGS. 13B and 13C may be performed only when the criteria forthe sleep mode are satisfied as described above in connection with step516.

The infusion pump 10 incorporates another power-saving feature in thatthe backlight 220 for the display 16 is activated only under certainconditions. If either a key on the keypad 14 is pressed or a visualalarm message is generated on the display 16, the routine 700 causes thebacklight 220 to be activated, via the control line 222, when theambient light fails to surpass a predetermined threshold, as detected bythe ambient light sensor 18.

Referring to FIG. 14, which is a flowchart of the backlight turn-onroutine 700, if there is an alarm as determined at step 702, the programbranches to step 704 where the ambient light sensor 18 is read (afterthe sensor 18 is powered up via the control line 328 connected to thepower switch 326). If the amount of ambient light detected by the sensor18 does not surpass a predetermined light threshold as determined atstep 706, then the backlight 220 is turned on at step 708 via thecontrol line 222 connected to the backlight 220. At step 710, abacklight timer, which causes the backlight 220 to be turned on only fora predetermined period of time, is then reset.

If no alarm was present as determined at step 702, then the programbranches to step 712 which determines whether a key has been pressed. Ifso, then the program performs steps 704-710 to turn on the backlight 220if the ambient light does not surpass a threshold level, as describedabove.

If no key has been pressed (and no alarm is present), the programbranches to step 714. Steps 714-720 cause the backlight 220 to beautomatically turned off after a predetermined period of time asdetermined by the backlight timer. At step 714, if the backlight is on,the program branches to step 716 where the backlight timer isincremented (the routine 700 is performed periodically, such as every 20milliseconds). At step 718, if the backlight timer is at its limit,indicating that the predetermined period of time for which the backlight220 should be illuminated has elapsed, then the program branches to step720 where the backlight 220 is turned off.

During programming and operation, the infusion pump 10 automaticallyrecords in the non-volatile memory 208 all significant infusion data togenerate a complete historical data record which can be later retrievedfrom the memory 208 and used for various purposes, including clinicalpurposes to aid in determining how effective a particular infusiontherapy was and treatment purposes to confirm that the prescribedinfusion was actually delivered.

FIG. 15 illustrates various steps at which infusion data is recordedthat are performed during the overall pump operation shown generally inFIG. 9. The infusion data recorded in the memory 208 is set forth inTable 1 below. A number of events which trigger the storage of data arelisted in the left-hand column of Table 1, and the infusion data that isrecorded upon the occurrence of each event is listed in the right-handcolumn of Table 1. The time at which the infusion data is recorded,which is determined by the real-time clock 210, is also stored alongwith the infusion data.

                  TABLE 1    ______________________________________    EVENT         DATA RECORDED    ______________________________________    Power On      Date and Time    Program       Infusion parameters. See Table 2.    Run           Infusion parameters. See Table 2.    Hold          Total Volume Infused    Restart       Time of Restart    Rate Changes  Total Volume Infused, Rate, Volume    Alarms        Total Volume Infused, Alarm Type    Infusion Complete                  Total Volume Infused    Malfunctions  Total Volume Infused, Malfunction Type    Resume        Infusion parameters. See Table 2.    Maintenance Date                  Date    Patient ID    Patient ID Number    Serial No.    Serial Number    Language Change                  New Language    Lockout       Modes Locked Out    Pressure Select                  New Pressure Setting    Bolus Request Given/Not Given, Bolus Amount    Titration     New Parameters    Power Off     Time of Power Off    Version No.   Software Version Number    ______________________________________

Referring to Table 1 and FIG. 15, when the power to the infusion pump 10is turned on, the date and time of the power turn-on is recorded. Whenthe pump is completely programmed pursuant to one of steps 420, 424,428, 432, 436 (FIG. 9) as determined at step 802, the programmedinfusion parameters are stored at step 804, along with the time of suchstorage. The particular parameters that are stored depend upon whichinfusion mode was programmed. Several examples of infusion parametersthat are stored for each of a number of infusion modes are illustratedin Table 2 set forth below.

                  TABLE 2    ______________________________________    INFUSION MODE    INFUSION PARAMETERS    ______________________________________    Continuous       Infusion Mode                     Infusion Rate                     Volume To Be Infused                     Delay Time                     Total Bag Volume                     KVO Rate    Auto-Ramp        Infusion Mode                     Infusion Rate                     Volume To Be Infused                     Delay Time                     Total Bag Volume                     Duration of Up-Ramp                     Duration of Down-Ramp                     KVO Rate    Intermittent     Infusion Mode                     Total Infusion Time                     Number of Doses                     Dose Time                     Dose Volume                     KVO Rate    ______________________________________

When the pump enters the run mode 460 (FIG. 9) as determined at step806, the time at which the run mode was begun, along with the parameterspursuant to which the infusion is performed, are stored at step 808.

At step 810, if the hold key is pressed, then the time at which the holdkey was pressed along with the total volume infused at the time the holdkey was pressed are stored at step 812. The pump also stores anyinfusion rate changes, such as changes caused by switching from acontinuous rate to a keep-vein-open (KVO) rate, or in the intermittentmode, changing from a KVO rate to a higher infusion rate, the presenceof which are detected at step 814. The new rate and the time at whichthe new rate started are stored at step 816.

At step 818, if any alarms are generated, the alarm type, the time atwhich the alarm occurred, and the total volume infused at the time ofthe alarm are recorded at step 820. If the infusion is completed asdetermined at step 822, the program branches to step 824 where the timeat which the infusion was completed is stored along with the totalvolume infused. At step 826, if there is a malfunction, the malfunctiontype, the time at which the malfunction occurred, and the total volumeinfused at the time of the malfunction are recorded at step 828.

At step 830, if the infusion is resumed (when the pump is turned back onafter having been turned off during an infusion), the time at which theinfusion is resumed along with the infusion parameters are stored atstep 832. Upon the completion of the programming of a lockout sequenceas determined at step 834 (i.e. after step 416 of FIG. 9), the time atwhich the programming of the lockout was completed is stored along withthe infusion modes that were locked out. At step 838, upon the detectionof a bolus request (via the bolus-request key 332 in FIG. 7), the timeat which the bolus was requested is stored, along with an indicationwhether the bolus was actually given and the amount of the bolus.

Modifications and alternative embodiments of the invention will beapparent to those skilled in the art in view of the foregoingdescription. This description is to be construed as illustrative only,and is for the purpose of teaching those skilled in the art the bestmode of carrying out the invention. The details of the structure andmethod may be varied substantially without departing from the spirit ofthe invention, and the exclusive use of all modifications which comewithin the scope of the appended claims is reserved.

What is claimed is:
 1. A cassette adapted to be insertable into aninfusion pump having a rotary pump wheel and removable from saidinfusion pump, said cassette comprising:a housing having a length, awidth, and a height, said housing having an upper surface with a firstaperture formed therein, said length of said housing being about sixtimes said height of said housing, said height of said housing beingabout twice said width of said housing; a length of flexible tubingsupported by said housing; a first vertically movable member having afirst surface and a second surface, said first surface having a portionwhich is arcuate in shape and adapted to substantially conform with apath of rotation defined by said rotary pump wheel of said infusionpump, said second surface being disposed within said aperture formed insaid upper surface of said housing so that said first vertically movablemember may be vertically displaced due to physical contact with saidsecond surface of said first vertically movable member; a secondvertically movable member disposed in said housing, said secondvertically movable member having a slot formed therein, a portion ofsaid flexible tubing being disposed within said slot, said secondvertically movable member being movable between a clamped position inwhich said flexible tubing is clamped to prevent any substantial liquidflow therethrough and an unclamped position in which substantial liquidflow through said flexible tubing is enabled; and a spring for biasingsaid second vertically movable member to said clamped position.
 2. Acassette as defined in claim 1 wherein said upper surface of saidhousing has a second aperture formed therein and wherein said secondvertically movable member has an upper portion which extends throughsaid second aperture to an elevation higher than said upper surface ofsaid housing when said second vertically movable member is disposed insaid clamped position.
 3. A cassette as defined in claim 1 wherein saidupper surface of said first vertically movable member is curved.
 4. Acassette as defined in claim 1 wherein said spring comprises a helicallycoiled spring.
 5. A cassette as defined in claim 1 additionallycomprising means for maintaining said second vertically movable memberin said unclamped position.
 6. A cassette as defined in claim 1 whereinsaid second vertically movable member has a first bore formed thereinand where said housing has a second bore formed therein, said cassetteadditionally comprising a pin which is insertable through said first andsecond bores to maintain said second vertically movable member in saidunclamped position.
 7. A cassette as defined in claim 1 additionallycomprising an enclosure coupled to said housing, said enclosure having abottom portion with a bore formed therein, said second verticallymovable member having a portion which extends through said bore in saidenclosure when said second vertically movable member is disposed in saidunclamped position.
 8. A cassette adapted to be insertable into andremovable from an infusion pump, said cassette comprising:a housingadapted to be insertable into and removable from said infusion pump; alength of flexible tubing supported by said housing; a verticallymovable member disposed in said housing, said vertically movable memberhaving a slot formed therein, a portion of said flexible tubing beingdisposed within said slot, said vertically movable member being movablebetween a clamped position in which said flexible tubing is clamped toprevent any substantial liquid flow therethrough and an unclampedposition in which substantial liquid flow through said flexible tubingis enabled; and means for automatically causing said vertically movablemember to move to said clamped position when said housing is removedfrom said infusion pump.
 9. A cassette as defined in claim 8 whereinsaid housing has an upper surface with an aperture formed therein andwherein said vertically movable member has an upper portion whichextends through said aperture to an elevation higher than said uppersurface of said housing when said vertically movable member is disposedin said clamped position.
 10. A cassette as defined in claim 8 whereinsaid spring comprises a helically coiled spring.
 11. A cassette asdefined in claim 8 additionally comprising means for maintaining saidvertically movable member in said unclamped position.
 12. A cassetteadapted to be insertable into and removable from an infusion pump, saidcassette comprising:a housing; a length of flexible tubing supported bysaid housing; a vertically movable member disposed in said housing, saidvertically movable member having a slot formed therein, a portion ofsaid flexible tubing being disposed within said slot, said verticallymovable member being movable between a clamped position in which saidflexible tubing is clamped to prevent any substantial liquid flowtherethrough and an unclamped position in which substantial liquid flowthrough said flexible tubing is enabled; and a spring for biasing saidvertically movable member to said clamped position, wherein saidvertically movable member has a first bore formed therein and whereinsaid housing has a second bore formed therein, said cassetteadditionally comprising a pin which is insertable through said first andsecond bores to maintain said vertically movable member in saidunclamped position.
 13. A cassette adapted to be insertable into andremovable from an infusion pump, said cassette comprising:a housing; alength of flexible tubing supported by said housing; a verticallymovable member disposed in said housing, said vertically movable memberhaving a slot formed therein, a portion of said flexible tubing beingdisposed within said slot, said vertically movable member being movablebetween a clamped position in which said flexible tubing is clamped toprevent any substantial liquid flow therethrough and an unclampedposition in which substantial liquid flow through said flexible tubingis enabled; a spring for biasing said vertically movable member to saidclamped position; and an enclosure coupled to said housing, saidenclosure having a bottom portion with a bore formed therein, saidvertically movable member having a portion which extends through saidbore in said enclosure when said vertically movable member is disposedin said unclamped position.
 14. A cassette as defined in claim 8 whereinsaid housing has a length, a width, and a height, wherein said length ofsaid housing is about six times said height of said housing, and whereinsaid height of said housing is about twice said width of said housing.15. A cassette adapted to be insertable into an infusion pump having arotary pump wheel and removable from said infusion pump, said cassettecomprising:a housing having a length, a width, and a height and beingadapted to be insertable into and removable from said infusion pump,said housing having an upper surface with an aperture formed therein; alength of flexible tubing supported by said housing; a verticallymovable member having a first surface and a second surface, said firstsurface having a portion which is arcuate in shape and adapted tosubstantially conform with a path of rotation defined by said rotarypump wheel of said infusion pump, said second surface being disposedwithin said aperture formed in said upper surface of said housing sothat said vertically movable member may be vertically displaced due tophysical contact with said second surface of said vertically movablemember.
 16. A cassette as defined in claim 15 wherein said upper surfaceof said vertically movable member is curved.
 17. A cassette as definedin claim 15 wherein said length of said housing is at least about fivetimes said height of said housing and wherein said height of saidhousing is at least about twice said width of said housing.
 18. Acassette as defined in claim 8 wherein said means for automaticallycausing said vertically movable member to move to said clamped positionwhen said housing is removed from said infusion pump comprises a springfor biasing said vertically movable member to said clamped position.